1. Field of the Invention
The invention concerns a corrugated gear.
The conventional corrugated gears are generally known under the name "Harmonic Drive". In these harmonic drive gears there is within a rigid or fixed support ring, which has a cylindrical, inwardly geared support surface, an outwardly geared, radially flexible roller bushing, which for example via a suitable drive device is elliptically deformed. Inward to outward gearing differs by one or more teeth. The geared rim of the radially flexible roller bushing is pressed by a, for example, elliptically deformed drive core of a drive unit, against the cylindrical, internally geared support surface of the rigid support ring. On the basis of the differential tooth count between support surface and roller bushing there is a permanent, continuous displacement of the circumferences which engage with each other. One entire rotation of the drive shaft brings about hereby only a further movement of the roller bushing about the predetermined differential of the tooth count between support ring and roller bushing. The harmonic-drive unit can thus achieve a very high rate of reduction.
2. Description of the Related Art
One example of such a gear is described in DE 38 15 118 A1. For deformation of the roller bushing a drive shaft is provided, upon which in the circumference direction a drive element with elliptical or at least essentially elliptical cross section is fixedly seated. The roller bushing is provided rotatably or as the case may be slidably upon this drive element by means of roller bearings. In place of the roller bearings another type of mounting, for example a sliding bearing, can be provided. As a result of the elliptical design of the mentioned drive element the roller bushing is likewise elliptically deformed and oppositely lying positions are brought into engagement with the internal teething of the rigid support ring.
An alternative embodiment of the reduction gear described in this document has a planetary gear unit as the drive device within the roller bushing. This is comprised of a first sun gear provided on the drive shaft and driven thereby, and on the outer circumference thereof at two oppositely lying positions to planetary gears are in engagement. These planetary gears are rotatably mounted on a framework which is rotatably mounted on the drive shaft. The roller bushing is pressed against the inner surface of the support ring at two oppositely lying positions by the planetary gears, so that a gear engagement occurs at these positions.
The driven side is so designed in this previously known gear, that the roller bushing exhibits an elongated area in the direction of the drive shaft. This elongated area is fixedly connected with a transmission element which is mounted rotatable and concentric to the support ring via pegs or journals. The pegs are radially oriented in the elongated area of the roller bushing and engaged in recesses in the respective other of the two elements. The already mentioned transmission element is connected with the drive shaft fixed against rotation. By such a solution an influence of the transmission element upon the deformed roller bushing is avoided so that a comparatively more compact construction of the total gear unit can be achieved.
A problem with this previously known gear is the fact that the drive shaft rotates with the same speed as the roller bushing. The overall reduction with this gear is thus limited.
A further gear, which operates on the manner of a harmonic drive gear, is known from WO97/08008. The drive unit for deforming the roller bushing is comprised of a plurality of essentially radially extending spokes or push rods of the same length, as transmission elements, which are supported upon a so-called "eccentric" drive core, in particular elliptic shaped or triangular, wherein the inner circumference of the drive core has a substantially smaller diameter than in the roller bushing which is basically cylindrical and radially flexible. The individual spokes or transmission elements or as the case may be planet arms move radially outwardly during rotation of the elliptical or triangular drive core and then again inwards. The spokes or planetary arms quasi "pulsate", which brings about a corresponding pulsation of the roller bushing. For this reason in the following the term "pulsator" will be employed in general for spokes or planetary arms, that is, for transmission elements.
This "pulsator" is subjected to strong torque production in the case of large gears, that is, the individual spokes or planetary arms can buckle. Further, is has been shown in practice, that the known "pulsator" causes noise.